Structural Epilepsy in Flat-Faced Dogs? MRI Shows Brachycephalic Breeds at Higher Risk

Prevalence of structural and idiopathic epilepsy in brachycephalic and non-brachycephalic dogs in the context of the International Veterinary Epilepsy Task Force guidelines

A. Prodger, S. Khan, G. Harris

Background
Epilepsy is a common neurological disorder in dogs, with structural epilepsy (SE) and idiopathic epilepsy (IE) being the predominant causes. The International Veterinary Epilepsy Task Force (IVETF) provides a tiered diagnostic system for IE, but does not currently consider brachycephaly as a risk factor. This study aimed to determine whether brachycephalic breeds are more predisposed to SE compared to non-brachycephalic breeds, and whether age at diagnosis differs between these groups.

Methods
This retrospective study reviewed 111 dogs presenting for generalized seizures at a UK referral center between 2015 and 2020. Dogs were categorized by skull type, interictal neurological status, and MRI findings. SE was diagnosed based on identifiable structural lesions (SL) on MRI, while IE was a diagnosis of exclusion. Statistical comparisons included Mann–Whitney U tests and Bayesian analyses to assess associations between brachycephaly, lesion prevalence, and age at diagnosis.

Results
SE was diagnosed in 34.2% of dogs overall, with a notably higher prevalence in brachycephalic dogs (61.8%) compared to non-brachycephalic dogs (22.1%). Among dogs aged 6 months to 6 years with normal interictal exams, 33.3% of brachycephalic dogs had SE versus 0% of non-brachycephalics. Median age at SE diagnosis was significantly younger in brachycephalics (60 months) compared to non-brachycephalics (108 months). The most common SLs in young brachycephalic dogs were inflammatory lesions and intra-axial neoplasms.

Limitations
This single-center retrospective study relied on medical records and MRIs without routine CSF analysis, potentially underestimating the prevalence of SE, particularly inflammatory causes. Some neurologic evaluations were not performed at the time of imaging, and classification of skull conformation was approximate, especially for crossbreeds. The exclusion of focal seizures may have limited detection of certain epilepsy subtypes.

Conclusions
Brachycephalic dogs are significantly more likely to have structural causes of seizures, even in the absence of neurological deficits and within the age window typically associated with IE. These findings support a recommendation to include brain MRI and CSF analysis in the diagnostic workup of brachycephalic dogs presenting with seizures, even if they otherwise meet tier I criteria for IE. This highlights the need to re-evaluate current epilepsy guidelines with consideration of breed-specific risk factors.

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